Method for producing ceramic sintered body, ceramic sintered body, and light emitting device

ABSTRACT

Provided are a method for producing a ceramic sintered body having improved light emission intensity, a ceramic sintered body, and a light emitting device. The method for producing a ceramic sintered body comprises preparing a molded body that contains a nitride fluorescent material having a composition containing: at least one alkaline earth metal element M 1  selected from the group consisting of Ba, Sr, Ca, and Mg; at least one metal element M 2  selected from the group consisting of Eu, Ce, Tb, and Mn; Si; and N, wherein a total molar ratio of the alkaline earth metal element M 1  and the metal element M 2  in 1 mol of the composition is 2, a molar ratio of the metal element M 2  is a product of 2 and a parameter y and wherein y is in a range of 0.001 or more and less than 0.5, a molar ratio of Si is 5, and a molar ratio of N is 8, and wherein the nitride fluorescent material has a crystallite size, as calculated by X-ray diffraction measurement using the Halder-Wagner method, of 550 Å or less, and calcining the molded body at a temperature in a range of 1,600° C. or more and 2,200° C. or less to obtain a sintered body.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This is a divisional application of U.S. patent application Ser. No.16/695,702, filed Nov. 26, 2019, which claims priority to JapanesePatent Application No. 2018-225511, filed on Nov. 30, 2018, thedisclosure of which is hereby incorporated reference in its entirety.

BACKGROUND Technical Field

The present disclosure relates to a method for producing a ceramicsintered body, a ceramic sintered body, and a light emitting device.

Description of Related Art

Alight emitting device using a light emitting element such as an LED oran LD is constituted by combining a light emitting element serving as anexcitation light source and a member containing a fluorescent materialthat absorbs a part of light emitted from the light emitting element andconverts the wavelength of the light to a different wavelength. Thelight emitting device emits mixed color light of the light emitted fromthe light emitting element and the light emitted from the fluorescentmaterial. Such a light emitting device is being utilized in a widevariety of fields such as light emitting devices for vehicles and indoorlighting, backlight sources for liquid crystal display devices,illuminations, and light source devices for projectors. In thisspecification, the “fluorescent material” is used in the same meaning asa “fluorescent phosphor”.

Examples of the fluorescent material may include a fluorescent materialcapable of emitting yellow to green light by the excitation lightemitted from the light emitting element, and a fluorescent materialcapable of emitting red light. Examples of the fluorescent materialcapable of emitting yellow or green light may include a rare earthaluminate fluorescent material, a silicate fluorescent material, and aCa-α-SiAlON fluorescent material. Examples of the fluorescent materialcapable of emitting red light may include a nitride-based fluorescentmaterial using europium as an activating element, and a fluoride-basedfluorescent material using manganese as an activating element.

As a member containing a fluorescent material, for example, JapaneseUnexamined Patent Publication No. 2014-234487 discloses a sintered bodycontaining an inorganic fluorescent material obtained by mixing an oxideserving as a binder, such as glass powder, with an inorganic fluorescentmaterial powder, and melting the binder, followed by solidifying.International Unexamined Patent Publication No. 2016/117623 discloses asintered body containing a fluoride inorganic binder and a nitridefluorescent material.

However, in the sintered body disclosed in Japanese Unexamined PatentPublication No. 2014-234487, the oxide serving as a binder reacts withthe fluorescent material at the time of forming the sintered body, andthe fluorescent material may not emit light or may hinder the lightemission. In the sintered body disclosed in International UnexaminedPatent Publication No. 2016/117623, the fluoride inorganic binder mayreact with the nitride fluorescent material to adversely affect thelight emission characteristics of the nitride fluorescent material.

Thus, the present disclosure has an object to provide a method forproducing a ceramic sintered body having improved light emissionintensity without adversely affecting the light emission characteristicsof a fluorescent material, a ceramic sintered body, and a light emittingdevice.

SUMMARY

The present disclosure includes the following embodiments.

A first embodiment of the present disclosure is a method for producing aceramic sintered body including

preparing a molded body that contains a nitride fluorescent materialhaving a composition containing: at least one alkaline earth metalelement M¹ selected from the group consisting of Ba, Sr, Ca, and Mg; atleast one metal element M² selected from the group consisting of Eu, Ce,Tb, and Mn; Si; and N, wherein a total molar ratio of the alkaline earthmetal element M¹ and the metal element M² in 1 mol of the composition is2, a molar ratio of the metal element M² is a product of 2 and aparameter y wherein y is in a range of 0.001 or more and less than 0.5,a molar ratio of Si is 5, and a molar ratio of N is 8, and wherein thenitride fluorescent material has a crystallite size, as calculated byX-ray diffraction measurement using the Halder-Wagner method, of 550 Åor less, and

calcining the molded body at a temperature in a range of 1,600° C. ormore and 2,200° C. or less to obtain a sintered body.

A second embodiment of the present disclosure is a ceramic sintered bodythat is composed of a nitride fluorescent material having a compositioncontaining: at least one alkaline earth metal element M¹ selected fromthe group consisting of Ba, Sr, Ca, and Mg; at least one metal elementM² selected from the group consisting of Eu, Ce, Tb, and Mn; Si; and N,wherein a total molar ratio of the alkaline earth metal element M¹ andthe metal element M² in 1 mol of the composition is 2, a molar ratio ofthe metal element M² is a product of 2 and a parameter y wherein y is ina range of 0.001 or more and less than 0.5, a molar ratio of Si is 5,and a molar ratio of N is 8, wherein the relative density of the ceramicsintered body is 80% or more.

A third embodiment of the present disclosure is a light emitting devicecomprising the ceramic sintered body and an excitation light sourcehaving a light emission peak wavelength in a range of 380 nm or more and570 nm or less.

In accordance with the above embodiments, a method for producing aceramic sintered body having improved light emission intensity withoutadversely affecting light emission characteristics of a fluorescentmaterial, a ceramic sintered body, and a light emitting device, can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart describing exemplary steps in a method forproducing a ceramic sintered body according to the present disclosure.

FIG. 2 is a graph showing light emission spectra of ceramic sinteredbodies according to Examples 1 and 2, and Comparative Example 1.

DETAILED DESCRIPTION

The method for producing a ceramic sintered body, the ceramic sinteredbody, and the light emitting device according to the present disclosurewill be hereunder described on the basis of embodiments. The embodimentsdescribed below are exemplifications for embodying the technical idea ofthe present invention, and the present invention is not limited to thefollowing method for producing a ceramic sintered body, ceramic sinteredbody, and light emitting device. Standards according to JapaneseIndustrial Standard (JIS) Z8110 are applied to the relations betweencolor names and chromaticity coordinates, the relations betweenwavelength ranges of light and color names of monochromatic lights, andthe like.

Method for Producing Ceramic Sintered Body

The method for producing ceramic sintered body includes preparing amolded body that contains a nitride fluorescent material having acomposition containing: at least one alkaline earth metal element M¹selected from the group consisting of Ba, Sr, Ca, and Mg; at least onemetal element M² selected from the group consisting of Eu, Ce, Tb, andMn; Si; and N, in which a total molar ratio of the alkaline earth metalelement M¹ and the metal element M² in 1 mol of the composition is 2, amolar ratio of the metal element M² is a product of 2 and a parameter ywherein y is in a range of 0.001 or more and less than 0.5, a molarratio of Si is 5, and a molar ratio of N is 8, and wherein the nitridefluorescent material has a crystallite size, as calculated by X-raydiffraction measurement using the Halder-Wagner method, of 550 Å orless, and calcining the molded body at a temperature in a range of1,600° C. or more and 2,200° C. or less to obtain a sintered body.

FIG. 1 is a flowchart describing one example of steps in the method forproducing a ceramic sintered body. Steps in the method for producing aceramic sintered body will be described by reference to FIG. 1. Themethod for producing a ceramic sintered body includes a molded bodypreparing step S102 and a calcining step S103. The method for producinga ceramic sintered body may include a nitride fluorescent materialpreparing step S101 of preparing a nitride fluorescent material having acrystallite size of 550 Å or less prior to the molded body preparingstep S102, and may include a processing step S104 after the calciningstep S103. The calcining step may include two or more calcining steps,such as a primary calcining step and a secondary calcining step.

The ceramic sintered body can be obtained by constituting a molded bodyusing a nitride fluorescent material having a crystallite size, ascalculated by X-ray diffraction measurement using the Halder-Wagnermethod, of 550 Å or less, and calcining the molded body at a temperaturein a range of 1,600° C. or more and 2,200° C. or less. The crystallitesize represents the size of an aggregation that can be regarded as asingle crystal. The larger the value of the crystallite size, the betterthe crystallinity. The nitride fluorescent material having a crystallitesize of 550 Å or less has a relatively low crystallinity. By forming amolded body using the nitride fluorescent material having a relativelylow crystallite size of 550 Å or less and calcining the molded body at atemperature in a range of 1,600° C. or more and 2,200° C. or less, thenumber of voids in the resulting ceramic sintered body is reduced, thatis, the relative density is increased, and a ceramic sintered bodyhaving high light emission intensity can be obtained. Although thereason why the light emission intensity of the resulting ceramicsintered body is increased is not clear, it is presumed that, since thenitride fluorescent material having a relatively small crystallite sizehas a part where the crystal structure can be changed, the molded bodythus formed is calcined at a temperature in a range of 1,600° C. or moreand 2,200° C. or less to change the part of the crystal structure, andthe number of voids in the molded body is reduced, so that the lightemission intensity becomes high. In certain examples, the molded bodycontains no binder composed of a fluoride or oxide. Oxygen contained inthe molded body is less than 3% by mass with respect to 100% by mass ofthe molded body. Fluorine contained in the molded body is less than 1%by mass with respect to 100% by mass of the molded body. In such a case,it may be presumed that, since the molded body contains no bindercomposed of a fluoride or oxide, the nitride fluorescent materialcontained in the molded body does not react with the binder even whenthe molded body is calcined at a temperature in a range of 1,600° C. ormore and 2,200° C. or less, the composition of the nitride fluorescentmaterial is not adversely affected by the calcination, and the lightemission intensity may not be reduced. When the crystallite size of thenitride fluorescent material is more than 550 Å, the light emissionintensity of the nitride fluorescent material itself becomes higher thanthat of the nitride fluorescent material having a crystallite size of550 Å or less. However, when the molded body is formed using the nitridefluorescent material having a crystallite size of more than 550 Å, thecrystallinity of the nitride fluorescent material itself is good, andthus the relative density of the resulting sintered body is converselylow, that is, a large number of voids are contained therein even whencalcining the molded body at a temperature in a range of 1,600° C. ormore and 2,200° C. or less. Since the voids promote light scattering,the amount of light extracted to the outside of the ceramic sinteredbody is also reduced, and the light emission intensity is lowered.

In order to enhance the relative density of the ceramic sintered bodyafter calcining the molded body, the crystallite size of the nitridefluorescent material constituting the molded body is 550 Å or less, andpreferably 500 Å or less, more preferably 480 Å or less, even morepreferably 450 Å or less. In order to improve the crystallinity of thenitride fluorescent material contained in the ceramic sintered body tosome extent after calcining the molded body, the crystallite size of thenitride fluorescent material constituting the molded body is preferably200 Å or more, more preferably 250 Å or more, even more preferably 300 Åor more.

As for the crystallite size of the nitride fluorescent material, XRD(X-ray diffraction) of the nitride fluorescent material is measuredusing an X-ray diffraction apparatus (for example, Ultima IV,manufactured by Rigaku Corporation). The measurement data is thenanalyzed by analysis software PDXL (manufactured by Rigaku Corporation)using No. 01-085-0101 of the ICDD (International Center for DiffractionData) card of Ba₂Si₅N₈ single phase, and the crystallite size can becalculated according to the Halder-Wagner method.

Preparation of Nitride Fluorescent Material

The method for producing a ceramic sintered body preferably includes astep of preparing a nitride fluorescent material having a crystallitesize of 550 Å or less. It is preferred that the nitride fluorescentmaterial having a crystallite size of 550 Å or less can be obtained by:preparing a raw material mixture that contains a first compoundcontaining at least one alkaline earth metal element M¹ selected fromthe group consisting of Ba, Sr, Ca, and Mg, a second compound containingat least one metal element M² selected from the group consisting of Eu,Ce, Tb, and Mn, and a compound containing Si; and heat-treating the rawmaterial mixture at a temperature in a range of 980° C. or more and1,680° C. or less in an atmosphere containing nitrogen.

In the nitride fluorescent material, crystallization of the obtainednitride fluorescent material can be suppressed by heat-treating the rawmaterial mixture at a temperature lower than the temperature at whichthe raw material mixture is heat-treated for obtaining the nitridefluorescent material, preferably at a temperature in a range of 980° C.or more and 1,680° C. or less, to thereby obtain the nitride fluorescentmaterial having a crystallite size of 550 Å or less. The temperature forheat-treating the raw material mixture is more preferably in a range of1,000° C. or more and 1,670° C. or less, even more preferably in a rangeof 1,200° C. or more and 1,660° C. or less, still more preferably in arange of 1,300° C. or more and 1,650° C. or less, particularlypreferably in a range of 1,350° C. or more and 1,650° C. or less.

The atmosphere for heat-treating the raw material mixture is preferablyan atmosphere containing nitrogen, or an inert atmosphere containingnitrogen. The content of nitrogen gas in the atmosphere forheat-treating the raw material mixture is preferably 70% by volume ormore, more preferably 80% by volume or more.

The pressure in the atmosphere for heat-treating the raw materialmixture is preferably in a range of 0.2 MPa or more and 2.0 MPa or less,more preferably in a range of 0.8 MPa or more and 1.0 MPa or less interms of gauge pressure. By setting the atmosphere for heat-treating theraw material mixture to a pressurized atmosphere, decomposition of thecrystal structure in the obtained nitride fluorescent material can besuppressed even in the case of obtaining a nitride fluorescent materialhaving a crystallite size of 550 Å or less and a relatively lowcrystallinity.

The time for heat-treating the raw material mixture can be appropriatelyselected depending on the heat-treating temperature and the pressure ofthe atmosphere at the time of heat-treating, and is preferably in arange of 0.5 hour or more and 20 hours or less, more preferably in arange of 1 hour or more and 10 hours or less, even more preferably in arange of 1.5 hours or more and 9 hours or less. When the heat-treatingtime is in a range of 0.5 hour or more and 20 hours or less,decomposition of the obtained nitride fluorescent material can besuppressed even in the case of obtaining a nitride fluorescent materialhaving a crystallite size of 550 Å or less and a relatively lowcrystallinity.

Examples of the first compound containing at least one alkaline earthmetal element M¹ selected from the group consisting of Ba, Sr, Ca, andMg may include hydrides, nitrides, fluorides, oxides, carbonates, andchlorides each containing an alkaline earth metal element M¹. Since thefirst compound containing an alkaline earth metal element M¹ containsfew impurities, hydrides, nitrides, or fluorides containing an alkalineearth metal element M¹ are preferred, and nitrides are more preferred.The first compound may contain a trace amount of at least one elementselected from the group consisting of Li, Na, K, B, and Al. The at leastone element selected from the group consisting of Li, Na, K, B, and Alcontained in the first compound is less than 1000 ppm by mass withrespect to the total amount of the first compound. Specific examples ofthe first compound containing an alkaline earth metal element M¹ mayinclude BaH₂, Ba₃N₂, BaF₂, SrH₂, Sr₃N₂, Sr₂N, SrN, SrF₂, CaH₂, Ca₃N₂,CaF₂, MgH₂, Mg₃N₂, and MgF₂. As the compound containing an alkalineearth metal element M¹, one kind of a compound containing one alkalineearth metal element M¹ selected from the group consisting of Ba, Sr, Ca,and Mg may be used; two or more kinds of compounds each containing onealkaline earth metal element M¹ may be used; or two or more kinds ofcompounds each containing two or more different alkaline earth metalelements M¹ may be used.

Examples of the second compound containing at least one metal element M²selected from the group consisting of Eu, Ce, Tb, and Mn may includehydrides, nitrides, fluorides, oxides, carbonates, and chlorides eachcontaining a metal element M². Since the second compound containing ametal element M² contains few impurities, hydrides, nitrides, orfluorides containing a metal element M² are preferred, and nitrides aremore preferred. Specific examples of the second compound containing ametal element M² may include EuH₃, EuN, EuF₃, CeH₃, CeN, CeF₃, TbH₃,TbN, TbF₃, MnN₂, MnN₅, and MnF₂. As the compound containing a metalelement M², one kind of a compound containing one metal element M²selected from the group consisting of Eu, Ce, Tb, and Mn may be used;two or more kinds of compounds each containing one metal element M² maybe used; or two or more kinds of compounds each containing two or moredifferent metal elements M² may be used.

The compound containing Si may be a metal substantially containing Sialone, or may be an alloy of Si where a part of Si is substituted withat least one metal selected from the group consisting of Ge, Sn, Ti, Zr,Hf, B, Al, Ga, and In. Examples of the compound containing Si mayinclude oxides, nitrides, fluorides, imide compounds, and amidecompounds. Since the compound containing Si contains few impurities,nitrides, imide compounds, amide compounds, or fluorides are preferred,and nitrides are more preferred. Specific examples of the compoundcontaining Si may include SiO₂, Si₃N₄, SiF₄, Si(NH)₂, Si₂N₂NH, andSi(NH₂)₄.

From the viewpoint of reactivity of each raw material and controllingparticle diameter during and after the heat-treatment, the averageparticle diameter of each raw material is preferably in a range of about0.1 μm or more and 10 μm or less, more preferably in a range of about0.1 μm or more and 5μm or less. The average particle diameter refers toFisher Sub-Sieve Sizer's number measured by Fisher Sub-Sieve Sizermethod.

The raw material mixture may contain a flux. When the raw materialmixture contains a flux and the generation temperature of the liquidphase of the compound contained as the flux is substantially the same asthe temperature in the heat-treatment, the reaction between the rawmaterials can be promoted by the flux. The flux is preferably a halidein order to promote the reaction between the raw materials. As thehalide to be used as the flux, a chloride or a fluoride of rare earthmetal, alkaline earth metal, or alkali metal can be used. The flux canbe added as a part of the raw materials of the fluorescent material byadjusting the amount such that the elemental ratio of the cationcontained in the flux becomes a part of the desired composition of thefluorescent material, or the flux can be added thereto after adjustingthe raw materials to be the desired composition of the fluorescentmaterial.

When the raw material mixture contains a flux, in order to obtain anitride fluorescent material having a desired crystallite size, forexample, the content of the flux in the raw material mixture ispreferably 10% by mass or less, more preferably 5% by mass or less basedon 100% of the raw material mixture.

The weighed raw materials may be mixed in wet or in dry using a mixingmachine to obtain a raw material mixture. As the mixing machine, a ballmill which is generally industrially used, as well as a grinding machinesuch a vibration mill, a roll mill, or a jet mill can be used, and theraw materials can be ground to enlarge the specific surface area. Inorder to adjust the specific surface area of the powder in a certainrange, the raw materials can be classified using: a wet separator suchas a sedimentation tank, a hydrocyclone, or a centrifugal separator; ora dry classifier such as a cyclone or an air separator, which aregenerally industrially used.

The raw material mixture can be set in a crucible or a boat made ofcarbon such as graphite, boron nitride (BN), alumina (Al₂O₃), tungsten(W), molybdenum (Mo), and heat-treated in a furnace to obtain a nitridefluorescent material.

The nitride fluorescent material obtained by heat-treating the rawmaterial mixture may be subjected to post-treatments such as grinding,dispersion, solid-liquid separation, and drying. The solid-liquidseparation can be performed by an ordinary industrial method such asfiltration, suction filtration, pressure filtration, centrifugation, ordecantation. The drying can be performed using an ordinary industrialapparatus such as a vacuum drier, a hot air heating drier, a conicaldrier, or a rotary evaporator.

The obtained nitride fluorescent material preferably has a compositionrepresented by the following formula (I).

(M¹ _(1−y)M² _(y))₂Si₅N₈   (I)

wherein M¹ represents at least one element selected from the groupconsisting of Ba, Sr, Ca, and Mg; M² represents at least one elementselected from the group consisting of Eu, Ce, Tb, and Mn; and ysatisfies 0.001≤y<0.5.

The obtained nitride fluorescent material may have a compositionrepresented by the following formula (II).

(Ba_(1−x−y)M¹² _(x)M² _(y))₂Si₅N₈   (II)

wherein M¹² represents at least one element selected from the groupconsisting of Sr, Ca, and Mg; M² represents at least one elementselected from the group consisting of Eu, Ce, Tb, and Mn; and x and ysatisfy 0≤x<1.0, 0.001≤y<0.5, and 0.001≤x+y<1.0 respectively. It ispreferred that 0<x<1.0 is satisfied.

The product of the parameter y and 2 represents a molar ratio of atleast one metal element M² selected from the group consisting of Eu, Ce,Tb, and Mn in 1 mol of the chemical composition of the nitridefluorescent material. The metal element M² is an activator of thenitride fluorescent material. From the viewpoint of obtaining a ceramicsintered body having high light emission intensity, the parameter y ispreferably in a range of 0.001 or more and less than 0.5 (0.001≤y<0.5),more preferably in a range of 0.005 or more and 0.4 or less(0.005≤y≤0.4), even more preferably in a range of 0.007 or more and 0.3or less (0.007≤y≤0.3), still more preferably in a range of 0.01 or moreand 0.2 or less (0.01≤y≤0.2). The “molar ratio” refers to a molar amountof the element in 1 mol of the chemical composition contained in thefluorescent material.

As shown in the formula (II), in the case of containing Ba and at leastone alkaline earth metal element M¹² selected from the group consistingof Sr, Ca, and Mg in the composition of the nitride fluorescentmaterial, the product of the parameter x and 2 represents a molar ratioof the alkaline earth metal element M¹² in 1 mol of the composition ofthe nitride fluorescent material. The parameter x is, though dependingon the amount of the activator, preferably in a range of 0 or more and0.75 or less (0≤x≤0.75), more preferably in a range of 0.01 or more and0.6 or less (0.01≤x≤0.60), even more preferably in a range of 0.05 ormore and 0.5 or less (0.05≤x≤0.50).

The average particle diameter (Fisher Sub-Sieve Sizer's number) of theobtained nitride fluorescent material, as measured according to theFisher Sub-Sieve Sizer method (hereinafter also referred to as “FSSSmethod”) is preferably less than 5.0 μm. When the average particlediameter of the nitride fluorescent material, as measured according tothe FSSS method, is less than 5.0 μm, a molded body having few voids canbe formed. The average particle diameter of the nitride fluorescentmaterial, as measured according to the FSSS method, is more preferably4.5 μm or less, even more preferably 4.0 μm or less; and may be 0.1 μmor more, or may also be 0.5 μm or more. The FSSS method is a type of anair permeability method and a method for measuring a specific surfacearea by utilizing the flow resistance of air to determine a particlediameter.

Preparation of Molded Body

In the step of preparing a molded body, the molded body is preferablyformed of a nitride fluorescent material having a crystallite size of550 Å or less for obtaining a sintered body having high relativedensity. The molded body is preferably composed of only a nitridefluorescent material having a crystallite size of 550 Å or less. Thatis, the content of the nitride fluorescent material having a crystallitesize of 550 Å or less in the molded body is preferably 100% by mass. Themolded body may contain voids in addition to the nitride fluorescentmaterial having a crystallite size of 550 Å or less, and the content ofthe nitride fluorescent material having a crystallite size of 550 Å orless may be 95% by mass or more, 97% by mass or more, 98% by mass ormore, 99% by mass or more, or 99.5% by mass or more.

In the molded body preparing step, the nitride fluorescent materialhaving a crystallite size of 550 Å or less is molded into a desiredshape to obtain a molded body. As the method for molding a molded body,a known method, such as a press molding method in which the powder ismolded by pressing, or a slurry molding method in which a slurrycontaining the powder is prepared to obtain a molded body from theslurry, can be employed. Examples of the press molding method mayinclude a die press molding method and a cold isostatic pressing(hereinafter also referred to as “CIP”) method that is specified in No.2109 of JIS Z2500:2000. As for the molding method, the two types ofmethods may be employed for forming the shape of the molded body, andthe CIP treatment may be performed after the die press molding. In theCIP treatment, the molded body is preferably pressed using water as amedium.

The pressure in the die press molding is preferably in a range of 5 MPaor more and 50 MPa or less, more preferably in a range of 5 MPa or moreand 20 MPa or less, even more preferably in a range of 5 MPa or more and15 MPa or less in terms of gauge pressure. When the pressure in the diepress molding is in the above range, the molded body can be formed intoa desired shape.

The pressure in the CIP treatment is preferably in a range of 50 MPa ormore and 250 MPa or less, more preferably in a range of 100 MPa or moreand 200 MPa or less. When the pressure in the CIP treatment is in theabove range, the density of the molded body is increased, and a moldedbody having a substantially uniform density on the whole can beobtained, thereby increasing the density of a sintered body obtained inthe following calcining step.

Calcining Step

The calcining step is a step of calcining a molded body at a temperaturein a range of 1,600° C. or more and 2,200° C. or less to obtain asintered body. By calcining a molded body containing a nitridefluorescent material having a crystallite size of 550 Å or less at atemperature in a range of 1,600° C. or more and 2,200° C. or less, thenumber of voids contained in the molded body is reduced to increase therelative density, and a ceramic sintered body having high light emissionintensity can be obtained.

In order to further improve the crystallinity of the nitride fluorescentmaterial having a crystallite size of 550 Å or less and a relatively lowcrystallinity and to suppress the decomposition of the crystalstructure, the temperature in the calcining step is preferably in arange of 1,600° C. or more and 2,100° C. or less, more preferably in arange of 1,600° C. or more and 2,000° C. or less, even more preferablyin a range of 1,600° C. or more and 1,900° C. or less, still morepreferably in a range of 1,600° C. or more and 1,800° C. or less.

Examples of the calcining method may include an atmospheric sinteringmethod in which the calcining is performed under a non-oxidizingatmosphere without applying pressure or load, a pressurized atmosphericsintering method in which the calcining is performed under a pressurizednon-oxidizing atmosphere, a hot-press sintering method, and a sparkplasma sintering (SPS) method. The non-oxidizing atmosphere refers to anatmosphere in which an amount of oxygen is several hundred ppm by volumeor less.

The calcining step is preferably performed in an atmosphere containingnitrogen gas. The atmosphere containing nitrogen gas is preferably anatmosphere containing at least 99% by volume of nitrogen. The atmospherecontaining nitrogen gas preferably contains nitrogen in an amount of 99%by volume or more, more preferably 99.5% by volume or more. Theatmosphere containing nitrogen gas may contain a trace amount of anothergas, such as oxygen, in addition to nitrogen, and the content of oxygenin the atmosphere containing nitrogen gas is preferably 1% by volume orless, more preferably 0.5% by volume or less, even more preferably 0.1%by volume or less, still more preferably 0.01% by volume or less,particularly preferably 0.001% by volume or less. The atmosphere in thecalcining step may also be a nitrogen-containing atmosphere having areducing property, or may be an atmosphere containing hydrogen gas andnitrogen. In the case of containing hydrogen gas in the atmospherecontaining nitrogen in the calcining step, the content of the hydrogengas in the atmosphere is preferably 1% by volume or more, morepreferably 5% by volume or more, even more preferably 10% by volume ormore. The calcining atmosphere may also be a reductive atmosphere usinga solid carbon in an air atmosphere.

By calcining a molded body in the atmosphere containing nitrogen gas, aceramic sintered body having high relative density, which contains anitride fluorescent material having high light emission intensity, canbe obtained. This may be because, for example, when the metal element M²serving as an activator is Eu, the ratio of divalent Eu²⁺ capable ofcontributing light emission is increased in the nitride fluorescentmaterial. The divalent Eu²⁺ is readily oxidized into a trivalent Eu³⁺,but by calcining a molded body in a highly-reductive atmosphere, thetrivalent Eu³⁺ of the nitride fluorescent material contained in themolded body may be reduced into the divalent Eu²⁺. Therefore, the ratioof the divalent Eu²⁺ contained in the nitride fluorescent material isincreased, so that a ceramic sintered body containing a nitridefluorescent material having high light emission intensity can beobtained.

The atmospheric pressure in the calcining step is preferably in a rangeof 0.1 MPa or more and 2.0 MPa or less, more preferably in a range of0.2 MPa or more and 1.5 MPa or less, even more preferably in a range of0.5 MPa or more and 1.2 MPa or less. The atmospheric pressure ispreferably a gauge pressure. When the atmospheric pressure in thecalcining step is in the above range, the crystallinity of the nitridefluorescent material having a crystallite size of 550 Å or less and arelatively low crystallinity is improved, and the decomposition of thecrystal structure is suppressed, so that a ceramic sintered bodycontaining a nitride fluorescent material having high emission intensitycan be obtained.

The calcining time may be appropriately selected depending on theatmospheric pressure. For example, the calcining time is in a range of0.5 hour or more and 20 hours or less, and preferably in a range of 1hour or more and 10 hours or less.

The calcining step may include two or more calcining steps, such as aprimary calcining step and a secondary calcining step. In the case ofcontaining two or more calcining steps, a ceramic sintered body obtainedby a primary calcining step may be subjected to secondary calcining at atemperature in a range of 1,400° C. or more and 2,200° C. or lessaccording to a hot isostatic pressing (hereinafter also referred to as“HIP”) method that is specified in No. 2112 of JIS Z2500:2000. Byfurther subjecting a ceramic sintered body obtained by primary calciningto secondary calcining according to the HIP treatment, the density ofthe ceramic sintered body can be further increased, and a ceramicsintered body capable of emitting light having a desired light emissionpeak wavelength with less chromaticity unevenness through irradiation ofthe excitation light can be obtained. The secondary calciningtemperature is preferably in a range of 1,600° C. or more and 2,100° C.or less in order to suppress the decomposition of the crystal structurein the nitride fluorescent material.

In the case of performing the secondary calcining according to the HIPtreatment, the pressure in the HIP treatment is preferably in a range of50 MPa or more and 300 MPa or less, more preferably in a range of 80 MPaor more and 200 MPa or less. When the pressure in the HIP treatment isin the above range, the whole of the ceramic sintered body can haveuniform and higher density without deteriorating the crystal structureof the nitride fluorescent material contained in the sintered body.

For example, the time for performing the secondary calcining may be in arange of 0.5 hour or more and 20 hours or less, and preferably in arange of 1 hour or more and 10 hours or less.

Processing Step

The method for producing a ceramic sintered body may include a step ofprocessing the resulting ceramic sintered body. Examples of theprocessing step may include a step of cutting the resulting ceramicsintered body into a desired size. A known method can be utilized forthe method for cutting a ceramic sintered body, and examples thereof mayinclude blade dicing, laser dicing, and wire sawing. Among others, wiresawing is preferred since the cut surface becomes flat with highaccuracy. By the processing step, a ceramic sintered body having adesired thickness and size can be obtained. The thickness of the ceramicsintered body is not particularly limited, but is preferably in a rangeof 1 μm or more and 1 mm or less, more preferably in a range of 10 μm ormore and 800 μm or less, even more preferably in a range of 50 μm ormore and 500 μm or less, still more preferably in a range of 100 μm ormore and 400 μm or less in consideration of the mechanical strength andthe efficiency of wavelength conversion.

Relative Density of Ceramic Sintered Body

The relative density of the resulting ceramic sintered body ispreferably 80% or more, more preferably 85% or more, even morepreferably 90% or more, still more preferably 91% or more. The relativedensity of the ceramic sintered body may be 100%, may be 99% or less, ormay be 98% or less. When the relative density of the resulting ceramicsintered body is 80% or more, the density of the ceramic sintered bodybecomes high, the number of voids is reduced, and light scattering dueto the voids is suppressed, so that a ceramic sintered body having highlight emission intensity can be produced.

In the present specification, the relative density of the ceramicsintered body refers to a value calculated by an apparent density of theceramic sintered body relative to a true density of the ceramic sinteredbody. The relative density is calculated by the following calculationformula (1).

$\begin{matrix}{{{Relative}\mspace{14mu}{density}\mspace{14mu}(\%)\mspace{14mu}{of}\mspace{14mu}{ceramic}\mspace{14mu}{sintered}\mspace{14mu}{body}} = {\frac{{Apparent}\mspace{14mu}{density}\mspace{14mu}{of}\mspace{14mu}{ceramic}\mspace{14mu}{sintered}\mspace{14mu}{body}}{{True}\mspace{14mu}{density}\mspace{14mu}{of}\mspace{14mu}{ceramic}\mspace{14mu}{sintered}\mspace{14mu}{body}} \times 100}} & (1)\end{matrix}$

The true density of the ceramic sintered body refers to a value obtainedby multiplying the mass ratio (% by mass) of the nitride fluorescentmaterial by the true density of the nitride fluorescent material,relative to 100% by mass of the ceramic sintered body. When the ceramicsintered body is composed of only the nitride fluorescent material, thetrue density of the ceramic sintered body is equal to the true densityof the nitride fluorescent material.

The apparent density of the ceramic sintered body refers to a valueobtained by dividing the mass of the ceramic sintered body by the volumeof the ceramic sintered body, which is determined by the Archimedes'method, and is calculated by the following calculation formula (2). Inthe calculation formula (2), the volume of the ceramic sintered bodyrefers to a volume determined by the Archimedes' method.

$\begin{matrix}{{{Apparent}\mspace{14mu}{density}\mspace{14mu}\left( \text{g/cm}^{3} \right)\mspace{14mu}{of}\mspace{14mu}{ceramic}\mspace{14mu}{sintered}\mspace{14mu}{body}} = \frac{{Mass}\mspace{14mu}(g)\mspace{14mu}{of}\mspace{14mu}{ceramic}\mspace{14mu}{sintered}\mspace{14mu}{body}}{{Volume}\mspace{14mu}\left( {cm}^{3} \right)\mspace{14mu}{of}\mspace{14mu}{ceramic}\mspace{14mu}{sintered}\mspace{14mu}{body}}} & (2)\end{matrix}$

Ceramic Sintered Body

The ceramic sintered body is a ceramic sintered body that comprises oris composed of a nitride fluorescent material having a compositioncontaining: at least one alkaline earth metal element M¹ selected fromthe group consisting of Ba, Sr, Ca, and Mg; at least one metal elementM² selected from the group consisting of Eu, Ce, Tb, and Mn; Si; and N,in which a total molar ratio of the alkaline earth metal element M¹ andthe metal element M² in 1 mol of the composition is 2, a molar ratio ofthe metal element M² is a product of 2 and a parameter y wherein y is ina range of 0.001 or more and less than 0.5, a molar ratio of Si is 5,and a molar ratio of N is 8, wherein the relative density is 80% ormore. The nitride fluorescent material contained in the ceramic sinteredbody may contain Ba and at least one alkaline earth metal element M¹²selected from the group consisting of Sr, Ca, and Mg as the alkalineearth metal element M¹. The molar ratio of the alkaline earth metalelement M¹² in 1 mol of the composition of the nitride fluorescentmaterial is preferably a product of a parameter x in a range of 0 ormore and 0.75 or less and 2. The ceramic sintered body may be composedof a nitride fluorescent material having a specific composition, and hasa high relative density of 80% or more. Therefore, the ceramic sinteredbody emits light having high light emission intensity and a desiredlight emission peak wavelength through irradiation of the excitationlight. The content of each element constituting the nitride fluorescentmaterial in the ceramic sintered body can be measured using aninductively coupled plasma (ICP) atomic emission spectroscopy, and thecomposition of the nitride fluorescent material can be determined fromthe results of the elemental analysis.

The ceramic sintered body is preferably composed of a nitridefluorescent material having a composition represented by the formula(I), and may be composed of a nitride fluorescent material having acomposition represented by the formula (II). When the ceramic sinteredbody is composed of a nitride fluorescent material having a compositionrepresented by the formula (I) or the formula (II), deterioration issuppressed as compared with a fluorescent member using a binder,durability is excellent, and high light emission intensity can bemaintained.

The relative density of the ceramic sintered body is 80% or more, andpreferably 85% or more, more preferably 90% or more, even morepreferably 91% or more. When the relative density of the ceramicsintered body is large, scattering of light due to voids is reduced, andthe light emission intensity becomes high. In addition, when therelative density of the ceramic sintered body is high, the ceramicsintered body may not be cracked or broken even in the case where theceramic sintered body is subjected to processing, such as cutting, andthe occurrence of chromaticity unevenness can be suppressed in the caseof using the ceramic sintered body for a light emitting device. Therelative density of the ceramic sintered body is more preferably 91% ormore. The relative density of the ceramic sintered body may be 100%, maybe 99.9% or less, or may be 99.8% or less.

Light Emitting Device

The light emitting device is constituted by combining the ceramicsintered body obtained by the above producing method and a lightemitting element such as an LED or an LD. The light emitting deviceconverts excitation light emitted from the light emitting element by theceramic sintered body, and emits light having a desired light emissionpeak wavelength. The light emitting device emits mixed light of thelight emitted from the light emitting element and the light of which thewavelength is converted by the ceramic sintered body. The light emittingdevice may be used in combination of a ceramic sintered body containingthe nitride fluorescent material and another ceramic sintered bodycontaining a fluorescent material other than the nitride fluorescentmaterial.

The light emitting element preferably has a light emission peakwavelength in a range of 380 nm or more and 570 nm or less, morepreferably in a range of 400 nm or more and 550 nm or less. For example,the light emitting element is preferably a semiconductor light emittingelement using a nitride-based semiconductor (In_(X)Al_(Y)Ga_(1−X−Y)N,0≤X, 0≤Y, X+Y≤1). Using a semiconductor light emitting element as anexcitation light source enables a high efficiency stable light emittingdevice that has high linearity of output relative to input and isresistant to mechanical shock to be obtained.

EXAMPLES

The present invention is hereunder specifically described by referenceto the following Examples. The present invention is not limited to theseExamples.

Example 1 Preparation of Nitride Fluorescent Material

Ba and Sr were used as alkaline earth metal elements M¹ contained in thenitride fluorescent material, and Eu was used as a metal element M².Ba₃N₂, Sr₃N₂, EuN, and Si₃N₄ were used as raw materials. The compoundsserving as raw materials were weighed in a glove box with an inert gasatmosphere such that a molar ratio of each element wasBa:Sr:Eu:Si=0.5:1.42:0.08:5 as a charged amount, and the compounds weremixed to obtain a raw material mixture. The resulting raw materialmixture was filled into a crucible, and heat-treated at a gas pressureof 0.9 MPa in terms of gauge pressure and a temperature of 1,400° C. for5 hours in an atmosphere containing nitrogen in an amount of 99.9% byvolume or more and oxygen (0.1% by volume or less) as the balance,thereby obtaining a sintered product. Since the particles of theresulting sintered product were sintered together, the sintered productwas subjected to wet dispersion followed by sieve classification toeliminate coarse particles and fine particles, thereby obtaining anitride fluorescent material having a composition of(Ba_(0.25)Sr_(0.71)Eu_(0.04))₂Si₅N₈ and having an average particlediameter shown in Table 1 with uniform particle diameter.

Preparation of Molded Body

The resulting nitride fluorescent material was filled into a die andpress-molded at a pressure of 7 MPa (71.38 kgf/cm²) to form acylindrical molded body having a diameter of 28.5 mm and a thickness of10 mm.

Calcining

The resulting molded body was placed in a calcining furnace(manufactured by Fuji Dempa Kogyo Co., Ltd.), and calcined whilemaintaining a temperature of 1,700° C. and a pressure of 0.9 MPa for 5hours in an atmosphere containing nitrogen in an amount of 99.9% byvolume or more and oxygen (0.1% by volume or less) as the balance,thereby obtaining a ceramic sintered body.

Example 2

A ceramic sintered body was obtained in the same manner as in Example 1except that the temperature for heat-treating the raw material mixturewas changed to 1,600° C. in the nitride fluorescent material preparingstep.

Comparative Example 1

A ceramic sintered body was obtained in the same manner as in Example 1except that the temperature for heat-treating the raw material mixturewas changed to 1,800° C. in the nitride fluorescent material preparingstep.

Average Particle Diameter of Fluorescent Material According to FSSSMethod

The average particle diameter (Fisher Sub-Sieve Sizer's number) of thenitride fluorescent material used in each of Examples and ComparativeExample was measured according to the FSSS method using a FisherSub-Sieve Sizer Model 95 (manufactured by Fisher Scientific Inc.). Theresults are shown in Table 1.

Light Emission Characteristics of Fluorescent Material Light EmissionSpectrum and Relative Light Emission Intensity (%)

The light emission characteristics of the nitride fluorescent materialin each of Examples and Comparative Example were measured. Using afluorospectrophotometer (product name: QE-2000, manufactured by OtsukaElectronics Co., Ltd.), each fluorescent material was irradiated withlight having an excitation wavelength of 450 nm to measure the lightemission spectrum thereof. The relative light emission intensity (%) atthe light emission peak wavelength of 630 nm, where the light emissionintensity of the obtained light emission spectrum was the maximum, wasdetermined. The relative light emission intensity (%) was calculatedwhen the light emission intensity at the light emission peak wavelengthof the nitride fluorescent material in Comparative Example 1 was set as100%. The results are shown in Table 1.

Luminescent Chromaticity x, y of Fluorescent Material

As for the nitride fluorescent material in each of Examples andComparative Example, the chromaticity x, y in chromaticity coordinatesof Commission international del'eclairage (CIE) 1931 color system wasmeasured using a quantum efficiency measurement system in thefluorospectrophotometer (product name: QE-2000, manufactured by OtsukaElectronics Co., Ltd.). The results are shown in Table 1.

XRD Measurement Crystallite Size (Å) of Fluorescent Material

As for the nitride fluorescent material in each of Examples andComparative Example, the XRD measurement (X-ray: CuKα, tube voltage: 40kV, tube current: 20 mA, scanning range: 10°≤2θ≤70°, radiation source:CuKα, scanning axis: 2θ/θ, measuring method: FP (fundamental parametermethod), counting unit: counts, step width: 0.02°, counting time: 10)was performed using an X-ray diffraction apparatus (product name: UltimaIV, manufactured by Rigaku Corporation). The measurement data was readusing analysis software PDXL (manufactured by Rigaku Corporation) andrefined using No. 01-085-0101 of the ICDD (International Center forDiffraction Data) card of Ba₂Si₅N₈ single phase, and the crystallitesize was then calculated according to the Halder-Wagner method (thewidth was corrected using an external standard sample). The results areshown in Table 1.

TABLE 1 Temperature for Light Emission XRD Heat-treating AverageCharacteristics Diffraction Raw Material Particle Relative LightCrystallite Mixture Diameter Chromaticity Emission Intensity Size (° C.)Composition (μm) x y (%) (Å) Example 1 1400(Ba_(0.25)Sr_(0.71)Eu_(0.04))₂Si₅N₈ 0.7 0.580 0.418 54.8 395 Example 21600 (Ba_(0.25)Sr_(0.71)Eu_(0.04))₂Si₅N₈ 1.1 0.584 0.415 71.7 435Comparative 1800 (Ba_(0.25)Sr_(0.71)Eu_(0.04))₂Si₅N₈ 5.8 0.599 0.401100.0 567 Example 1

Relative Density (%) of Ceramic Sintered Body

The relative density of the ceramic sintered body in each of Examplesand Comparative Example was calculated by the calculation formulae (1)and (2). The true density of the ceramic sintered body was equal to thetrue density of the nitride fluorescent material that formed the moldedbody in each of Examples and Comparative Example, and the true densityof the nitride fluorescent material was 4.36 g/cm³. The results areshown in Table 2.

Relative Light Emission Intensity (%) of Ceramic Sintered Body

The ceramic sintered body in each of Examples and Comparative Examplewas cut into a thickness of 300 μm using a wire saw to form a sample. AnLED chip composed of a nitride semiconductor having a light emissionpeak wavelength of 455 nm was used as a light source, and the sample ofthe ceramic sintered body was irradiated with light emitted from thelight source. Thereafter, the light emission spectrum in a wavelengthrange of 430 nm or more and 800 nm or less, which was obtained from thesample of the ceramic sintered body upon receiving the light emittedfrom the light source, was measured using the fluorospectrophotometer.The relative light emission intensity (%) at the light emission peakwavelength of 630 nm, where the light emission intensity of the obtainedlight emission spectrum was the maximum, was determined. The relativelight emission intensity (%) of the ceramic sintered body was calculatedwhen the light emission intensity at the light emission peak wavelengthof 630 nm, where the light emission intensity the ceramic sintered bodyin Comparative Example 1 was the maximum, was set as 100%. The resultsare shown in Table 2. In addition, FIG. 2 is a graph showing lightemission spectra of relative light emission intensity with respect tothe wavelengths in Examples 1 and 2, and Comparative Example 1, when theintegral value of the light emission spectrum in Comparative Example 1is set as 100%.

Luminescent Chromaticity x, y of Ceramic Sintered Body

As for the sample of the ceramic sintered body in each of Examples andComparative Example, the chromaticity x, y in chromaticity coordinatesof CIE 1931 color system was measured using the quantum efficiencymeasurement system in the fluorospectrophotometer (product name:QE-2000, manufactured by Otsuka Electronics Co., Ltd.). The results areshown in Table 2.

TABLE 2 Relative Relative Light Density Chromaticity Emission Intensity(%) x y (%) Example 1 97.0 0.676 0.322 623.1 Example 2 91.8 0.672 0.321369.2 Comparative Example 1 64.5 0.700 0.319 100.0

As shown in Table 2, the relative light emission intensity of theceramic sintered body in each of Examples 1 and 2 was higher than thatof the ceramic sintered body in Comparative Example 1. The nitridefluorescent material used for the ceramic sintered body in each ofExamples 1 and 2 had a crystallite size of 550 Å or less, and had lowcrystallinity even for a nitride fluorescent material. Thus, therelative light emission intensity of the nitride fluorescent materialitself was lower than that of the nitride fluorescent material used forthe ceramic sintered body in Comparative Example 1 having a crystallitesize of 550 Å or more. However, the ceramic sintered body obtained byforming a molded body using a nitride fluorescent material having acrystallite size of 550 Å or less and calcining the molded body at atemperature in a range of 1,600° C. or more and 2,200° C. or less had ahigh light emission intensity exceeding three times higher than that ofthe ceramic sintered body in Comparative Example 1 having a crystallitesize of 550 Å or more. Although the reason why the ceramic sintered bodyin each of Examples 1 and 2 had higher light emission intensity thanthat of the ceramic sintered body in Comparative Example 1 is not clear,it is presumed that, when the nitride fluorescent material having arelatively low crystallite size is calcined at a temperature in a rangeof 1,600° C. or more and 2,200° C. or less, the number of voids in theceramic sintered body is reduced and the light emission intensitybecomes high.

In contrast, the light emission intensity of the ceramic sintered bodyin Comparative Example 1 was lower than that of the ceramic sinteredbody in each of Examples 1 and 2. It is presumed that this is becausethe ceramic sintered body in Comparative Example 1 uses the nitridefluorescent material having good crystallinity with a crystallite sizeof more than 550 Å, the relative density of the ceramic sintered body islow, and a large number of voids are present therein.

The ceramic sintered body according to the present disclosure emitslight through irradiation of excitation light, and can be utilized as awavelength converting member capable of converting the wavelength oflight emitted from an LED or an LD, and a material for a solidscintillator.

The invention claimed is:
 1. A ceramic sintered body, comprising anitride fluorescent material having a composition containing: Si; N; atleast one alkaline earth metal element M¹ selected from the groupconsisting of Ba, Sr, Ca, and Mg; and at least one metal element M²selected from the group consisting of Eu, Ce, Tb, and Mn, in which atotal molar ratio of the alkaline earth metal element M¹ and the metalelement M² in 1 mol of the composition is 2, a molar ratio of the metalelement M² is a product of 2 and a parameter y wherein y is in a rangeof 0.001 or more and less than 0.5, a molar ratio of Si is 5, and amolar ratio of N is 8, wherein a relative density of the ceramicsintered body is 80% or more.
 2. The ceramic sintered body according toclaim 1, wherein the nitride fluorescent material has a compositionrepresented by the following formula (I):(M¹ _(1−y)M² _(y))₂Si₅N₈   (I) wherein M¹ represents at least onealkaline earth metal element selected from the group consisting of Ba,Sr, Ca, and Mg; M² represents at least one metal element selected fromthe group consisting of Eu, Ce, Tb, and Mn; and y satisfies 0.001≤y<0.5.3. The ceramic sintered body according to claim 1, wherein the nitridefluorescent material has a composition represented by the followingformula (II):(Ba_(1−x−y)M¹² _(x)M² _(y))₂Si₅N₈   (II) wherein M¹² represents at leastone element selected from the group consisting of Sr, Ca, and Mg; M²represents at least one element selected from the group consisting ofEu, Ce, Tb, and Mn; and x and y satisfy 0≤x<1.0, 0.001≤y<0.5, and0.001≤x+y<1.0 respectively.
 4. The ceramic sintered body according toclaim 1, wherein the relative density of the ceramic sintered body is90% or more, the relative density of the sintered body is calculated byan apparent density of the ceramic sintered body relative to a truedensity of the ceramic sintered body.
 5. The ceramic sintered bodyaccording to claim 1, wherein the ceramic sintered body is composed ofthe nitride florescent material.
 6. The ceramic sintered body accordingto claim 1, wherein the relative density of the ceramic sintered body is80% or more and 100% or less.
 7. A light emitting device, comprising:the ceramic sintered body according to claim 1, and an excitation lightsource having a light emission peak wavelength in a range of 380 nm ormore and 570 nm or less.